With each iteration of Windows, slews of articles come out related to optimal hardware for getting the performance out of the machine you desire. With XP, we saw a significant increase in optimal RAM, with figures of 1GB to 2GB, depending on usage, for a smooth desktop. With Vista, we're seeing a large jump again, with some citing that the "sweet spot" will be a massive 4GB.

Well, maybe not so massive anymore - afterall, 2GB memory kits are maybe half the price they were four years ago. That, coupled with Vista's "minimum" of 512MB and SuperFetch (a great expansion to Prefetch), may be sane reasoning for plugging 4GB into a system:

That's due in part to Windows SuperFetch, which takes data from the hard drive, stores it in the available RAM and makes it readily accessible to the processor. SuperFetch depends a great deal on user predictability and takes snapshots of user activity. If SuperFetch determines that an application is launched at a particular time, it will have it loaded into the available RAM. With more RAM, there's more caching and better software response, said Short.
Of course, don't expect "budget" systems to be able to fill that need anytime soon. Odds are, however, systems with 512MB and Vista will be few and far in between in the following months, as vendors realize that the minor cost increase moving to 1GB or even 2GB are easily offset by the boost in performance. Even king Dell is suggesting 2GB of RAM for a Vista system, along with Samsung. Some may lament the ever-bloating nature of PC software, but I am not surprised in the least.